88jx

I know there has been a lot of other threads about rough idle but i've tried almost everything and nothing has helped. It's an 88 with 4.0 AW4 just hit 100,000 over the last 5,000 miles replaced, cap+rotor, plugs+wires, 02 sensor, tps all fluids and filters, pcv valve, vacuum harness cleaned throttle body and iac. It's seems to run worse when the engines cold and if i rev the engine and then let off it will almost stall, but if im giving it gas it will run perfect it's only rough at idle whether im in park, reverse, neutral or drive any help would be appreciated
ive also ran seafoam through it a few times

Slim357

Id try a new cps and the upgraded bosch fuel injectors they may help. If you do a new cps go to Jeep and get it the ones from autozone or really any parts store suck the dont put out right. Dont know that that will help though mine is an 89' same motor and trans it idles kinda rough sometimes think its just a curse we have since we have the old motor. Sorry man

Guntar13

Not sure what kind of i2 sensor you put in but try a Bosch one. For some reason my 89 hates the ntk but really likes the Bosch. With the ntk the computer goes crazy and won't go to closed loop, causing a bad idle. The Bosch fixed er right up. Just a thought! Also make sure the tps was set dead accurate since that can cause all sorts of issues. Also ground refreshing look up cruiser54's threads about it, it's major important.

cruiser54

Did you adjust the new TPS? And if so, how?

Make sure your intake manifold bolts are snug. They tend to loosen up over time.

Good advice on where to purchase the CPS, but they usually cause a "crank- no start".

caged

try twisting the fuel injectors while the engine is running.
see if that changes the idle.

i would replace with sebring/cirrus 703 injectors.

Slim357

How can you tell when it goes into a closed loop whats the difference between open and closed loop?

Slim357

Mine spat and sputtered till i fixed mine have a budy with the H.O. Motor and he has the same issue b/c his isnt putting out the right volts at times.

cruiser54

Like Guntar13 suggested, do the following. He speaks from experience.

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011

88jx

i just tried twisting the fuel injectors while it was running and one of them sprayed out gas when i twisted it? I take it thats not suppose to happen. Also i forgot to mention that there has always been a slight hissing sound(possibly a vacuum leak) but i replaced and checked almost all my vacuum lines and that didn't help

cruiser54

Using throttle body cleaner, spray around the intake and injectors with the engine idling.

88jx

I sprayed around the injectors and the same one that sprayed gas when I moved it whenever I sprayed around the injector with throttlebody cleaner the hissing sound wood go away. Could that be a bad o ring in injector ? Thanks for all the replies I'm finally getting somewhere

XJ.89.Limited

Mine just started doing this the other day too. I think it's my tps acting up again. I'll start it, it'll start fine and rev to about 1200, then rev down like usual, but go down to the first line on the tach and sputter. It stalled once or twice, but usually just idles low. I've noticed my exhaust got a little louder too on the deep tones if that helps any. But again, this all only happens sometimes. It still starts fine and it runs like a champ.

caged

i would pull and replace at least that one injector.

but in all reality, i would just pull all the stock injectors and replace with junkyard 703 injectors from a mid-late 90's chrysler cirrus/sebring.
be sure to replace at least the upper o-rings with new ones. just a few cents from autozone, etc.
be sure to lube up those o-rings with vaseline or similar before you slip on the fuel rail.

88jx

I'll go to advanced auto tomorow and get some new o rings and see if that helps. How do u install the o rings?

cruiser54

Caged is trying to tell you something here. The factory original injectors were a fire hazard and should be replaced with upgraded injectors.